I think your facts are wrong. Teams within a division play the same interleague teams (all of the AL east played NL east this year), with the exception of the rival series. And I think they play other teams in their league the same, or at least very close. The lack of balance effects the comparison between teams of different divisions more so than teams within the same division. You play your division rivals twice as often as other teams in your league. The worst team in the AL east is 2 games under .500. So the Orioles play the same teams as the yankees, but have a much harder schedule than the white sox who get to play against three teams under .500. That calls into question whether the White Sox have really outplayed the O's, but its unquestionable that the Yankees have outplayed the O's.
So after 162 games, the yanks and O's have played almost the exact same schedule, and whoever wins the divison has proven the better team.
Yes, his facts were wrong and yours are correct. (But I agree with his argument) For all intents and purposes, teams within the same division play as similar a schedule as can be hoped for. (The divisions aren't equal - NL Central has 6 and AL West has 4 - so there are always minor variations)
But the bold part above is precisely why the wild card works and why I disagree with your earlier post (#31 - wild cards don't deserve to be there). The argument can easily be made that the O's "deserve" to be there just as much as the White Sox, and the wild card gives them that chance. It wasn't that long ago that the Padres (my Padres, so I ain't complaining!) won the NL West with an 82-80 record. it would be hard to argue that they "deserved" to be there more than the Braves (or whoever ended up winning the wild card that year) who certainly had a much better record.
And now the wild card is kind of the best of both worlds, because it gets you in, but you are "punished" and relegated to a crap-shoot one game playoff, rather than being put on equal footing with the division winners.